AURORA — The killer brought four guns — two semi-automatic pistols, an assault-style rifle and a shotgun — to the movie theater, where 70 people were shot or injured, of whom 12 died.

He also came dressed for battle, wearing a gas mask, a combat helmet, a ballistic vest and armor protecting his legs, throat and groin.

Law enforcement officials said Friday that they are investigating whether James Eagan Holmes, the 24-year-old suspect, was legally eligible to own all those weapons and combat gear. But they had found no evidence of a criminal history that would have prohibited him from buying the weapons used to massacre moviegoers at a midnight Batman premiere in Aurora.

His only run-in with police: an October 2011 speeding ticket.

Aurora Police Chief Daniel Oates said Holmes brought a pair of .40-caliber Glock pistols, an AR-15 military-style rifle and a Remington shotgun to the Century Aurora 16 complex, but it was unclear whether he used them all as he strode through the theater, shooting people apparently at random. One Glock pistol was found in his white Hyundai when police arrested him outside the car, he said. Oates said Holmes purchased 6,000 rounds of ammunition and multiple magazines, including a drum magazine able to hold 100 cartridges, from stores and on the Internet.

Oates also said investigators have not yet determined how many shots were fired or how many gun magazines were brought to the theater to carry out the midnight massacre.

But “many, many rounds were fired,” he said.

According to one law enforcement source, the gunman could easily have shot police officers as they approached because of all his combat gear but sat calmly by his car instead.

The AR-15 is a semi-automatic version of the military M-16 rifle, first marketed for civilian sales in 1963.

Glock, an Austrian gunmaker, has become the leading seller of semi-automatic pistols to U.S. law enforcement agencies and offers a variety of .40-caliber pistols to civilians as well.

The Remington Model 870 is a U.S.-made pump-action shotgun used by the public for sport shooting and hunting and is often carried by law enforcement and military personnel.

Convicted felons, people convicted of domestic violence and people who have been adjudicated as mentally defective or committed to a mental institution are among those prohibited from buying guns in the United States.

Though Holmes apparently purchased his legally, “There is a huge gun issue here,” said Kristen Rand, legislative director for the Violence Policy Center, a gun-control group.

From Columbine High to Virginia Tech to Fort Hood to the Aurora movie theater, mass murderers have brought “high-capacity magazines used either in pistols or assault rifles,” she said. “That is the common thread.”

Holmes wielded a variant of the AR-15 manufactured by Smith and Wesson that comes with a 30-round magazine, she said, and Glock “really drove the switchover from revolvers to semi-automatic pistols” in the American market.

On its website, Gun Owners of America, a group opposed to stricter gun laws, blamed Holmes’ ability to shoot so many people on the absence of guns in the audience.

“The gunman used a movie gunfight to cover his actions and further surprise the innocent patrons. Worse, the theater in Aurora reportedly has a ‘no guns’ policy,” the group stated. “Despite gun control’s obvious failure, the calls for more restrictions have already begun.”

Rand and Brad Beyersdorf, a spokesman for the Bureau of Alcohol, Tobacco, Firearms and Explosives in Denver, said they think people who have not been convicted of violent felonies can legally purchase the ballistic gear Holmes wore.

One of the pistols and the rifle were purchased at Gander Mountain in Thornton. The second pistol was bought at the Gander Mountain in Denver and the shotgun at the Denver Bass Pro Shop, according to Tom Mangan, a Phoenix-based agent with the ATF.

David Olinger is an investigative journalist who has worked for newspapers in New Hampshire, Florida and Colorado since 1976. In 18 years in Colorado, he has covered a variety of subjects for The Denver Post.

Today, one out of every three men imprisoned in Colorado -- and four out of every five women inmates -- say they have some type of moderate to critical mental health need, according to the Colorado Department of Corrections. The number of inmates with mental health needs in Colorado's prisons has steadily risen in the past two decades.

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